1. Field of the Invention
The invention relates to a method for the applying of patterns and symbols onto a polyolefin-coated imaging base paper.
2. Brief Description of the Background of the Invention Including Prior Art
The desired characters are conventionally applied with the aid of flexographic-printing or engraving-printing techniques onto the raw-base paper in order to be able to apply the names of the manufacturer or other characterizing features onto the back side of a polyolefin-coated imaging base paper and the printed side is then coated with a clear polyethylene.
In case of an absence of titanium dioxide in the back side polyolefin coating, the print picture appears clear and the overall required total opacity is achieved in general by the filling of the raw-base paper and a corresponding titanium dioxide addition into the polyethylene coating of the front face side. However, with some imaging base papers, there is required such a high opacity that a titanium dioxide addition is also required in the back side coating. However, based on this titanium dioxide addition, there occurs an interference with the legibility of the print picture.
In particular, two disadvantages occur when employing the conventional printing processes for this kind of characterizing and/or marking of base papers.
First, an automatic detection of defects and problems of the photographic paper becomes difficult with laser techniques, since these laser techniques can be influenced by the interference caused by the printed characters.
Second, the print characters can generate interfering effects relating to the final photographic picture, generated on the emulsion-coated side, based on photo-chemical reactions.
In addition, the use of conventional printing inks requires additional protective steps, which include avoiding or preventing a soiling and dirtying by the inks and suppressing an explosion danger associated with the solvent contained in the printing inks.
It has already been tried to characterize the polyolefin-coated photographic base paper by embossing. For this purpose, the polyethylene-coated paper was passed through a calender, where the roller of the calender was furnished with a specially structured surface. This way of operation has however proven to be unsuitable for this purpose, since no uniform stamping and impression depth could be achieved. In addition, the method required two separate operations, coating and stamping, which could not be performed in one single operational step.
In addition, a method exists in the art, where a chill cylinder roll, with a specially prepared surface, is employed for the application of different patterns or symbols onto the back side of a polyolefin-coated base paper, which chill cylinder roll allows the polyolefin-extrusion coating and the characterization in one single operational step, in-line.
This latter method is, for example, taught in the Japanese Patent JP No. 86-021,833, referenced for example in Agfa-Gevaert Fotobericht No. 23, 1988. The polyethylene is extruded through a slot between a pressure roll and a chill cylinder roll onto the carrier. The surface of the chill cylinder roll can be provided with different patterns, such as, for example, characters of all kinds, where the surface of the characters is distinguished by a different roughness than that of the chill cylinder roll itself.
A disadvantage of this method comprises that, during the later processing of the base paper, characterized according to this method and subsequently coated with photographic emulsion, there is observed a desensitization of the emulsion.
In addition, the legibility of the characters, obtained with the aid of the recited chill cylinder roll, is not particularly good.
It is a further disadvantage in the context of this method that the polyolefin coating mass obviously does not contain any titanium dioxide or other pigments, since pigmentation of the coating mass is desired in some photographic or reprographic products.